This invention relates to continuous power systems. In particular, the present invention relates to continuous power systems that utilize a source of stored thermal energy to provide a continuous supply of electric power when a primary power supply fails, or when deterioration occurs in the power being supplied to the end user.
Continuous power systems are often used to insure that, when a primary power supply fails due to equipment malfunction, downed lines or other reasons, electric power will continue to be supplied to critical loads such as telecommunication systems, because, for example, telecommunication systems often include facilities that may be in relatively isolated locations, such as a telecommunication repeater tower. Other applications of the present invention include hospital operating room equipment, computer systems and computerized manufacturing equipment. Continuous power systems avoid equipment failures, costly downtime and equipment damage.
Known continuous power systems may employ an uninterruptible power supply (UPS) to provide alternating current (AC) power to the end user or critical load, or may use other electronic means to provide DC power to the end user or critical load.
For known continuous power systems, batteries or flywheels may be employed as energy storage subsystems to provide bridging energy while a fuel-burning engine is started. Such flywheel systems may include a flywheel connected to an electrical machine that can operate both as a motor and a generator. For example, U.S. Pat. No. 5,731,645 describes flywheel systems that provide backup power to the load in UPS systems. The electrical machine is powered by a DC buss to operate as a motor when acceptable power is received from the primary power supply. When power from the primary power supply fails (or is degraded), the electrical machine is rotated by the kinetic energy of the flywheel and operates as a generator to supply power to the DC buss.
Continuous power systems often use prime movers (e.g., fuel-burning engines) to drive backup generators during prolonged power outages. These prime movers, however, are often costly, complicated, and may require extensive ongoing maintenance. In addition, the engines themselves may fail to start, resulting in a loss of power to the critical load. Moreover, some localities limit the running time or the number of starts per year for backup generator engines, thereby limiting the ability to test and maintain such systems.
Other energy storage systems currently used to provide backup power are often expensive and complicated. For example, in typical battery energy storage systems, there is a risk that undetected battery damage or corrosion of battery terminals can result in a failure to deliver backup power when needed. Moreover, batteries have a limited shelf life, in addition to requiring expensive ventilation, drainage, air conditioning and frequent maintenance. Flywheel energy storage systems, while avoiding most of the disadvantages of batteries, can be expensive since they are often mechanically complex and can require complicated power electronics.
Some known systems provide long-term power by driving a shaft-mounted generator with a turbine. For example, U.S. Pat. No. 6,255,743 (Application No. 09/318,728) describes an uninterruptible power supply system that includes a shaft-mounted generator and a turbine. These turbines may be open systems, where the turbine is driven by a fuel source that is regularly renewed, such as LP gas, methane, gasoline, diesel fuel. In such instances, the turbine exhaust is allowed to escape into the environment.
Other turbine systems, however, may be closed or partially-closed systems. In such systems, some or all of the turbine exhaust is recaptured by the system for later use. For instance, in a partially-closed system that is steam powered, the system may be configured to recapture a portion of the steam that is exhausted from the turbine. The system may then condense the steam (using a condenser or through natural cooling) into water prior to reheating, revaporizing and reusing the steam to drive the turbine.
In most closed systems, substantially all of the working fluid is condensed prior to reuse. The condensation is usually accomplished by using a condenser that cools the gas to a temperature at which the gas condenses into liquid form. In some systems, some of the liquid working fluid can be stored in a device, such as an accumulator, as heated or superheated liquid which can be evaporated and used to drive the turbine by use of its stored sensible heat.
Another concern with turbine systems relates to system efficiency. In such systems, it is often desirable to reuse thermal energy to the extent possible, rather than lose the energy to the environment. Accordingly, closed turbine systems can be arranged with an accumulator, preheater and evaporator interconnected so that working fluid is passed from one component to another throughout the whole system. These separate components, however, are not able to share significant amounts of stored heat energy. Rather, heat energy is often lost via radiation into the environment, other machinery, or even as the working fluid passes through the system.
Accordingly, it is an object of the present invention to provide continuous power system assemblies that reduce stored thermal energy losses.
It is another object of the present invention to provide continuous power system assemblies that utilize a single source of thermal energy to heat multiple components.
It is a further object of the present invention to provide components of a continuous power system that may be used as a source of stored thermal energy for short-term backup power needs.
The continuous power system assemblies of the present invention efficiently utilize thermal energy by minimizing overall heat loss. In particular, the assemblies of the present invention include an integrated unit that contains an accumulator and a preheater/evaporator for use with a turbine. The accumulator is used to store hot liquid working fluid prior to vaporization and injection into the turbine. The working fluid may, in accordance with the present invention, be preheated to a predetermined temperature by a heating element, such as a resistor assembly, that is immersed in the working fluid.
The accumulator is, in accordance with the present invention, located in the core of the integrated assembly. A series of preheater coils surround the accumulator housing, and are heated by thermal energy that is lost by the accumulator. A series of evaporator coils surround and are connected to the preheater coils. The evaporator coils may also be heated by thermal energy that escapes from the accumulator housing.
The preheater and evaporator coils are contained in an additional housing that includes a port for the introduction of heated gas from an external source, such as a fuel burning furnace. The preheater/evaporator housing is surrounded by an assembly housing, and a layer of insulation is located between the two housings to further minimize thermal energy losses by the assembly.
Thus, the present invention provides for the efficient storage of heat energy by surrounding the accumulator with the preheater and/or evaporator so that heat lost by the accumulator is used by other assembly components. Moreover, the heat energy lost by the accumulator may be more easily captured and utilized by the preheater and evaporator by thermally insulating the entire assembly, thereby minimizing heat energy losses to the environment.
In accordance with the methods of the present invention, an electric heating element (or other known heating device) is placed in good thermal contact with the accumulator. This heating element may be referred to simply as the xe2x80x9caccumulator heater,xe2x80x9d and may be driven by power sources other than electricity. The accumulator heater may be used to heat the liquid inside the accumulator during STAND-BY mode (i.e., when the power grid, or utility power, is providing sufficient power at a sufficient quality to the load).
During STAND-BY mode, it may be desired to seal the liquid in the accumulator from the other parts of the continuous power system. This may be accomplished, for example, by using valves. Preventing substantial flow of liquid into and out of the accumulator allows the accumulator heater to heat the liquid in the accumulator to a desired temperature and pressure (because the accumulator is likely sealed) for operation with the turbine when utility power becomes insufficient for the load, due to either quantity or quality.
Once the degradation of power is detected and such other stores of energy as may exist are at predetermined levels, the system switches to RUN mode, and the liquid in the accumulator is released by valve into the preheater and evaporator to power the turbine. It should be noted that an OUTAGE, as defined herein, includes both an interruption in power from a source (such as utility power), as well as a degradation in quality of the power delivered by the source. This includes both SHORT-TERMxe2x80x94in terms of seconds or minutes, and LONG-TERM, or EXTENDED OUTAGES (e.g., lasting hours, days, or even weeks).
It may be advantageous for the accumulator of the present invention to be a substantially cylindrical container. The accumulator heater may be an electric heating element that is placed inside of the accumulator and may be integral with the accumulator. The preheater and evaporator components may be formed as a coiled tube heat exchanger designed to heat a liquid, such as toluene, to a superheated vapor state. While the preheater of the present invention is shown wrapped helically around the accumulator and the evaporator is shown wrapped helically around the preheater, alternative arrangements, such as longitudinally arranged tubing sections, may be used.